Getting a Bleach Bypass Look in the Compositor
The "bleach bypass look" can be replicated in its most simplest way by reducing saturation and increasing contrast of the image using bright/contrast node.

But instead to get a more detailed look what I would suggest is to:


have the image de-saturated slightly
have a copy of the original image de-saturated completely and boost
the contrast of this layer by carefully using an RGB curves node
the monochrome layer should be mixed with the first image using
"overlay" blending mode.


To adjust the contrast effect you would adjust the curve as desired and also the factor/strength of the mix/overlay node.



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In your example image the artist appears to have also used some sort of sharpening or detail enhancement to make details pop out more.